Currently, an optical rotary encoder shown in FIG. 1 and FIG. 2 has been proposed. In these figures, 1 indicates a rotary driver and 2 indicates a rotating shaft. A driving force output from the rotary driver 1 is transmitted to an external device not shown through a gear 3 provided to the rotating shaft 2. 4 indicates an optical rotary encoder and its shaft 5 is projected externally and is coupled to the rotating shaft 2 through a jointer 6. The shaft 5 is rotatably supported by the ball bearings 7, 7 and a rotor 8 is fitted between these ball bearings 7, 7. The rotor 8 is composed of a fitting member 9 fixed to the shaft 5 and a disk 10 fixed thereto. The disk 10 is provided with plurality of slits (not shown) formed along the circumferencial direction. 11, 12 are respectively a light emitting element and a light sensing element and these are arranged face to face at the position of slit provided on the disk 10. The lead wires 13, 14 are connected to an electric circuit comprising an amplifier circuit, waveform shaping circuit etc., and an output from the light receiving element 12 is fed back to a control device (not shown) of the rotary driver 1 through such electrical circuit.
When the rotary driver 1 operates, a driving force is transmitted to external device and simultaneously the disk 10 in a rotary encoder 4 rotate. Therefore, the light emitted from the light emitting element 11 to the disk 10 passes intermittently through the disk 10 owing to the slits and the light is received by the light receiving element 12 as the light signal containing data of rotating speed of rotary driver 1. The light signal thus obtained is converted to an electrical signal by the light receiving element 12 and is fed back to a control device of the rotary driver 1 through an electrical circuit. Therefore, a rotating speed of the rotary driver 1 is controlled and accordingly operation of external device is controlled.
But, such a conventional optical rotary encoder is always accompanied by following disadvantages. Namely, since the shaft 5 of rotary encoder 4 has been coupled to a rotating shaft 2 of the rotary driver 1 through a jointer 6 which is provided for absorbing eccentricity of axial center, wider installation space has been required. In addition, the shaft 5 may not sometimes perfectly follow rotation of the rotating shaft 2.
Moreover, since the shaft 5 is supported by the ball bearings 7, 7, rotating torque and rotating speed are inevitably limited and simultaneously the shaft cannot bear the use for a long period of time.